This invention relates to an improvement of an electrolytic capacitor used for electronic devices.
A conventional electrolytic capacitor comprises a pair of electrode foils, an oxide layer provided on the surface of at least one of the electrode foils, an ion permeable capacitor paper interposed between the pair of electrode foils, a liquid electrolyte being impregnated into the capacitor paper, the lamination of the electrode foils and the capacitor paper being wound into a roll and hermetically sealed into a metal container with a gas permeable packing member, and a pair of lead wires led from each of the electrodes to outside of the container through the packing member.
Solutions of electrolytes such as a bolic acid or adipic acid solved in a solvent such as ethylene glycol or dimethyl formamide have been used as the electrolyte liquid. These solutions has an ion conduction property mainly through (OH).sup.- ion. When an alternate electric current flows through the capacitor, ions collide with the capacitor paper or the electrodes to generate oxygen and hydrogen through electrolysis. oxygen thus generated is usually absorbed by the electrodes thereby restoring the oxide layer. Hydrogen generated is, however, stored in the container resulting in a rise of inner pressure. The hydrogen is generated in proportion to the electric current, a temperature and a time and is discharged out of the container. The electrolyte is consumed in accordance with the discharge of the hydrogen. The capacitor ends its life when the electrolyte is exhausted.
An impedance characteristic is usually measured by means of flowing no signal currents. In operation of the capacitor, however, an alternate electric current flows through the capacitor. Ions move in accordance with an intensity of the electric current thereby generating hydrogen gas bubbles continuously. The bubbles stick to fibers constituting the capacitor paper thereby blocking the flow of the ion current. This phenomenon is remarkable at such low voltages as under the voltage of ten and several volts. This means that the ion conduction efficiency decreases. As a result, an internal impedance is greatly increased by the hydrogen gas generated in proportion to an electric current and a temperature when a signal current flows in the actual operation.
Those electrolytic capacitors, when used in a power supply for a high output power amplifiers, decrease an output power of the amplifier by the increase of the internal impedance in operation by more than ten times as high as the internal impedance at the time of measurement.
There has been no method for effectively solving the problem mentioned above. It has been tried to decrease the hydrogen gas by mixing the electrolyte with a liquid material reacting the hydrogen gas. Such liquid material, however, could not be used with enough amount because it degrades the electric or temperature characteristic of the electrolyte. Therefore, such liquid material has been hardly used for high quality electrolytic capacitors because it is acting rather harmfully. There has been also no effective means to cope with the problem of shortening of the life of the capacitor resulting from the generation of the gas.